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java(5) java(5)
NAME
java, javac, jre, jdb, javah, javap, javadoc, appletviewer, rmic, rmiregis-try, serialver, native2ascii, jar, javakey - The Java Development Kit
tools
SYNOPSIS
java [ options ] classname <args>
java_g [ options ] classname <args>
DESCRIPTION
This reference page describes the java command only. The Java Development
Kit (JDK) is part of the Java Virtual Machine (VM). If the JDK documenta-
tion was installed on your Tru64 UNIX system, you can view documentation on
all of the JDK tools, and other Java reference material, at the following
location:
/usr/share/doclib/java/index.html
The java command invokes an interpreter that executes Java bytecodes. It
executes Java class files created by a Java compiler, for instance, javac.
NOTES
Any arguments that appear after classname on the command line are passed to
the main method of the class.
The java command expects the binary representation of the class to be in a
file called classname.class, which is generated by compiling the
corresponding source file with javac. All Java class files end with the
filename extension .class which the compiler automatically adds when the
class is compiled. classname must contain a main method defined as follows:
class Aclass {
public static void main(String argv[]){
. . .
}
}
java executes the main method and then exits unless main creates one or
more threads. If any threads are created by main then java doesn't exit
until the last thread exits.
Ordinarily, you compile source files with javac then run the program using
java. However, java can be used to compile and run programs when the -cs
option is used. As each class file is loaded its modification date is com-
pared to the modification date of the class source file. If the source has
been modified more recently, it is recompiled and the new class file is
loaded. java repeats this procedure until all the classes are correctly
compiled and loaded.
The interpreter can determine whether a class is legitimate through the
mechanism of verification. Verification ensures prior to their execution
that class files do not violate any language constraints.
java_g is a non-optimized version of java suitable for use with debuggers
like jdb.
EXAMPLES
The classname argument is the name of the class to be executed. classname
must be fully qualified by including its package in the name, for example:
% java java.lang.String
When you define your own classes you need to specify their location. Use
CLASSPATH to do this. CLASSPATH consists of a colon separated list of
directories that specifies the path. For example:
.:/home/xyz/classes
The system always appends the location of the system classes onto the end
of the class path unless you use the -classpath option to specify a path.
OPTIONS
-debug Allows the Java debugger, jdb, to attach itself to this java
session. When -debug is specified on the command line, java
displays a password which must be used when starting the
debugging session.
-cs, -checksource
When a compiled class is loaded, this option causes the
modification time of the class bytecode file to be compared
to that of the class source file. If the source has been
modified more recently, it is recompiled and the new class
file is loaded.
-classpathpath
Specifies the path java uses to look up classes. Overrides
the default or the CLASSPATH environment variable if it is
set. Directories are separated by colons. Thus the general
format for path is:
.:<your_path>
00 For example:
.:/home/xyz/classes:/usr/local/java/classes
-mxx Sets the maximum size of the memory allocation pool (the
garbage collected heap) to x. The default is 16 megabytes of
memory. x must be greater than or equal to 1000 bytes.
By default, x is measured in bytes. You can specify x in
either kilobytes or megabytes by appending the letter k for
kilobytes or the letter m for megabytes.
-msx Sets the startup size of the memory allocation pool (the
garbage collected heap) to x. The default is 1 megabyte of
memory. x must be > 1000 bytes.
By default, x is measured in bytes. You can specify x in
either kilobytes or megabytes by appending the letter k for
kilobytes or the letter m for megabytes.
-noasyncgc Turns off asynchronous garbage collection. When activated no
garbage collection takes place unless it is explicitly
called or the program runs out of memory. Normally garbage
collection runs as an asynchronous thread in parallel with
other threads.
-noclassgc Turns off garbage collection of Java classes. By default,
the Java interpreter reclaims space for unused Java classes
during garbage collection.
-version Prints the build version information.
-help Prints a usage message.
-ssx Each Java thread has two stacks: one for Java code and one
for C code. The -ss option sets the maximum stack size that
can be used by C code in a thread to x. Every thread that is
spawned during the execution of the program passed to java
has x as its C stack size. The default units for x are
bytes. The value of x must be greater than or equal to 1000
bytes.
You can modify the meaning of x by appending either the
letter k for kilobytes or the letter m for megabytes. The
default stack size is 128 kilobytes (-ss128k).
-ossx Each Java thread has two stacks: one for Java code and one
for C code. The -oss option sets the maximum stack size that
can be used by Java code in a thread to x. Every thread that
is spawned during the execution of the program passed to
java has x as its Java stack size. The default units for x
are bytes. The value of x must be greater than or equal to
1000 bytes.
You can modify the meaning of x by appending either the
letter k for kilobytes or the letter m for megabytes. The
default stack size is 400 kilobytes (-oss400k).
-t Prints a trace of the instructions executed (java_g only).
-v-verbose Causes java to print a message to stdout each time a class
file is loaded.
-verify Runs the verifier on all code.
-verifyremote Runs the verifier on all code that is loaded into the system
via a classloader. verifyremote is the default for the
interpreter.
-noverify Turns verification off.
-verbosegc Causes the garbage collector to print out messages whenever
it frees memory.
-DpropertyName=newValue
Redefines a property value. propertyName is the name of the
property whose value you want to change and newValue is the
value to change it to. For example, this command line
% java -Dawt.button.color=green ...
sets the value of the property awt.button.color to "green".
java accepts any number of -D options on the command line.
ENVIRONMENT VARIABLES
CLASSPATH Used to provide the system a path to user-defined classes.
Directories are separated by colons, for example,
.:/home/xyz/classes:/usr/local/java/classes
SEE ALSO
If the JDK documentation was installed on your Tru64 UNIX system, you can
view it at the following location:
/usr/share/doclib/java/index.html